Starboard Port?
Larry,I am assuming you are taking about the thru-hull fitting above the water line. On our 376 we have(2)of them exactly where you are describing.(1) is for the water out circuit for our Adler Barber refrigeration.(2) is for the water out for our reverse cycle heat pump.More than likely, if you have either, that will be your answer. I think they are located under your joinery work that is a shelf above your dinette seat on the interior starboard side. We have a small nook in the corner that we can remove and get access to this area.No water will run from this port unless a)you open the seacock that provides inflow to the unit; and, b) you must have the red switch turned on for refrig; or, reverse cycle compressor is running! Mike DiMario Media, PAS/V SerenityH376